Some LAN (Local Area Network) application protocols, for example, DECnet LAT (Local Area Transport), IEEE LLC2 (Logical Link Control type 2), NetBios (NETwork Basic Input Output System), IBM SNA (Systems Network Architecture), are built on the assumption that the underlying network does not mis-order frames. As a result, even a low incidence of frame mis-ordering could result in perceived problems in networks that support these application protocols. For this reason, the IEEE 802.1D bridging standard specification explicitly forbids frame duplication and mis-ordering.
This requirement is relevant to the transparent LAN service that can be considered as an extended LAN to the end customers. Frame mis-ordering is particularly likely under network link or node failure conditions where rapid failure protection (e.g., under 50 ms) can be achieved through the use of explicitly routed paths such as MPLS (Multi Protocol Label Switching) traffic engineering LSPs (Label Switched Paths). In such a case, the perceived period of performance degradation of end-user applications due to frame mis-ordering—even a small amount—can be significantly longer than the actual restoration time of the network connectivity.
Systems and methods to prevent frame mis-ordering are required to deal with this situation.